Flame-retardant swim bladder adhesive and preparation method thereof

Abstract

The present application relates to a kind of preparation methods of fire-retardant water-resistant swim bladder adhesive, to solve the poor water resistance of swim bladder glue, the inconvenience of storage and the poor fire-retardant performance of the drawbacks, using phytic acid, urea, 5-hydroxymethyl furfural and other environmentally friendly materials to prepare environmentally friendly fire-retardant water-resistant non-formaldehyde resin-based bio-based adhesive, by multistage reaction to prepare the adhesive with good fire-retardant effect, environmentally friendly adhesive, such adhesive has broad application space in the field of cultural relics restoration, packaging materials, furniture, building.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and in particular to a fish swim bladder adhesive that combines flame retardant and water-resistant properties, and its preparation method. Technical Background Adhesives are indispensable basic materials in fields such as wood processing, furniture manufacturing, building decoration, packaging and printing, and cultural relic restoration. Currently, most synthetic adhesives widely used in the market, such as phenolic resins, urea-formaldehyde resins, melamine-formaldehyde resins, and polyurethanes, are made from petroleum resources. Furthermore, their production and use pose problems such as the release of free formaldehyde, emissions of volatile organic compounds, and isocyanate toxicity, which harm human health and the ecological environment. With increasingly scarce petroleum resources and ever-increasing demands for green environmental protection, the development of renewable, low-toxicity, and environmentally friendly bio-based adhesives has become a research hotspot in this field.

[0002] Fish maw glue is a natural protein adhesive obtained from fish swim bladders through processing. Its main component is collagen-derived gelatin macromolecules, rich in amino-containing side chains such as lysine and arginine, as well as a large number of hydroxyl and carboxyl groups. Derived from a byproduct of aquatic product processing, fish maw glue boasts significant advantages such as renewable raw materials, biodegradability, high bonding strength, and being non-toxic and formaldehyde-free. It has been used since ancient times in fields such as woodworking, musical instrument making, and calligraphy and painting mounting. However, as a modern industrial adhesive, fish maw glue still faces the following three bottlenecks: Firstly, it has poor flame retardant properties. Fish maw glue has a protein skeleton and is a flammable organic material with a low limiting oxygen index and a large heat release during combustion. It is difficult to meet the flame retardant requirements of materials in furniture, construction, rail transportation, and electronic appliances, posing a fire hazard.

[0003] Secondly, it has poor water resistance. Unmodified fish glue mainly relies on hydrogen bonds and intermolecular physical entanglement to form a glue. When it comes into contact with water or in a humid environment, it easily absorbs water, swells, or even re-dissolves. Its wet bonding strength is extremely low, and the wet strength retention rate is usually less than 10%, which seriously limits its application in humid environments.

[0004] Third, its processing performance is not easy to control. Fish maw gel has high gel strength, easily solidifies into a gel at room temperature, has poor fluidity, and is difficult to apply and coat. It needs to be liquefied to broaden its processing window.

[0005] Traditional methods for flame-retardant modification of protein-based adhesives often employ halogenated flame retardants or direct blending with additive flame retardants such as ammonium polyphosphate and triphenyl phosphate. Halogenated flame retardants release toxic hydrogen halide gases during combustion, contradicting environmental protection principles. Additive inorganic flame retardants have poor compatibility with the protein matrix, and when added in large quantities, they are prone to migration and precipitation, significantly weakening the adhesive strength. Furthermore, existing modification methods often only address one aspect of flame retardancy or water resistance, making it difficult to maintain high adhesive strength while simultaneously achieving both flame retardancy and water resistance.

[0006] In summary, existing protein-based adhesives generally suffer from drawbacks such as poor flame retardancy, poor water resistance, and decreased bond strength after modification, making it difficult to meet the requirements of green, environmentally friendly, safe, and reliable applications. Therefore, there is an urgent need in this field to develop an adhesive that uses renewable fish maw glue as the main material and possesses both excellent flame retardancy and water resistance, as well as its preparation method. Summary of the Invention

[0007] The technical problem solved by this invention is to provide a flame-retardant fish maw adhesive and its preparation method. This method uses fish maw adhesive as the main raw material. First, the pH of the fish maw adhesive is adjusted by a weak acid to achieve liquefaction. Then, 5-hydroxymethylfurfural undergoes a Schiff base condensation reaction with the amino groups on the side chains of the fish maw adhesive. A phytic acid-urea salt, prepared by the pre-reaction of phytic acid and urea, is introduced to construct a phosphorus-nitrogen synergistic char-forming flame-retardant system. Finally, triglycidyl ether-based polyfunctional epoxy compounds are used to covalently crosslink the protein chains, improving the water resistance and wet strength of the adhesive layer. The prepared fish maw adhesive maintains high bonding strength while possessing excellent flame-retardant and water-resistant properties. Furthermore, the preparation process does not use formaldehyde, isocyanates, or halogens, and the weak acids and bases used are volatile and leave no metal ion residue, making it environmentally friendly. Specifically, a method for preparing a flame-retardant fish maw adhesive includes the following steps: (1) Liquidation of fish maw glue: A certain amount of fish maw glue and deionized water are added to the reaction vessel and stirred thoroughly to make the fish maw glue swell and disperse evenly, to obtain mixture A; the pH value of mixture A is adjusted with a weak acid and heated and stirred until the fish maw glue is fully liquefied, to obtain liquefied fish maw glue solution B; (2) 5-hydroxymethylfurfural grafting modification: 5-hydroxymethylfurfural was added to the liquid fish glue solution B, and the mixture was heated and stirred under weak alkaline conditions to allow the aldehyde group of 5-hydroxymethylfurfural to undergo Schiff base condensation reaction with the amino group of the side chain of fish glue to obtain grafted modified fish glue solution C. (3) Preparation and introduction of phytic acid-urea salt: Phytic acid and urea are mixed in a certain molar ratio and heated and stirred to prepare a viscous phytic acid-urea salt mother liquor D; Mother liquor D is added to grafted modified fish glue solution C and stirred evenly to obtain flame retardant modified fish glue solution E. (4) Epoxy crosslinking and water-resistant modification: Triglycidyl ether epoxy compounds are added to flame-retardant modified fish maw glue solution E, and the mixture is heated and stirred under weak alkaline conditions to allow the epoxy groups to undergo ring-opening crosslinking reactions with the amino, hydroxyl, and carboxyl groups on the protein chain, thereby obtaining flame-retardant fish maw glue adhesive. Preferably, in step (1), the weight ratio of the fish maw glue to deionized water is 1:2 to 1:5, and the stirring speed is greater than 500 r / min; Preferably, in step (1), the weak acid is one or more of acetic acid, citric acid, and lactic acid; Preferably, in step (1), the adjusted pH value is 8 to 10, the heating temperature is 80°C to 100°C, and the liquefaction time is 60 min to 180 min; Preferably, in step (2), the amount of 5-hydroxymethylfurfural added is 5% to 15% of the mass of the fish maw glue; Preferably, in step (2), the temperature of the grafting modification reaction is 50°C to 70°C, the reaction time is 1 h to 3 h, and the pH value of the reaction system is 8.5 to 9.5; Preferably, in step (3), the molar ratio of phytic acid to urea is 1:4 to 1:8; Preferably, in step (3), the reaction temperature for preparing phytic acid-urea salt mother liquor D is 60°C to 80°C, and the reaction time is 3 h to 4 h. Preferably, in step (3), the amount of phytic acid-urea salt mother liquor D added is 10% to 40% of the mass of fish glue, based on phytic acid-urea salt solids; Preferably, in step (3), after adding the phytic acid-urea salt mother liquor D to the grafted modified fish maw gel solution C, the pH value of the system is adjusted back to 8 to 9 using a weak acid or a weak base; Preferably, in step (4), the triglycidyl ether epoxy compound is one or two of trimethylolpropane triglycidyl ether and glycerol triglycidyl ether; Preferably, in step (4), the amount of the triglycidyl ether epoxy compound added is 5% to 20% of the mass of the fish maw glue; Preferably, in step (4), the pH value of the reaction system is 8 to 10, the reaction temperature is 60°C to 80°C, and the reaction time is 1 h to 6 h.

[0008] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention uses fish maw glue, a renewable by-product of aquatic product processing, as the main raw material to replace petroleum-based synthetic adhesives. It does not produce free formaldehyde during preparation and use, and does not use isocyanates or halogens. It is green, environmentally friendly, low-toxic and safe.

[0009] (2) This invention introduces furan char-forming units by Schiff base reaction grafting of 5-hydroxymethylfurfural with fish glue, and constructs a phosphorus-nitrogen-carbon synergistic expansion char-forming flame retardant system with phytic acid-urea salt. During combustion, a dense expansion char layer is formed, which significantly improves the limiting oxygen index of fish glue, reduces the peak heat release rate and total heat release, and has obvious flame retardant effect.

[0010] (3) The present invention uses triglycidyl ether polyfunctional epoxy compounds to perform three-dimensional covalent crosslinking of protein chains, which greatly improves the wet strength retention rate and water resistance of the adhesive layer, and overcomes the defects of traditional fish maw glue that swells when exposed to water and has low wet strength.

[0011] (4) The flame retardant of the present invention is introduced in a reactive / salt-forming manner, which has good compatibility with the protein matrix and is not easy to migrate and precipitate. While imparting flame retardant properties, it has little impact on the bonding strength.

[0012] (5) The weak acid and weak base (acetic acid and ammonia) used in the liquefaction of this invention can be volatilized, and there are no metal ion residues in the system, which does not interfere with the char formation behavior of the flame retardant system. The whole process is carried out under normal to medium temperature conditions, without the need for high pressure equipment, and is easy to operate and simple. Detailed Implementation

[0013] To make the technical solution of the present invention clearer, the present invention will be further described below with reference to embodiments. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be construed as limiting the present invention; the performance data in the following embodiments are exemplary data, and the actual measured values ​​should be used in actual applications.

[0014] Example 1 (1) Liquefaction of fish maw glue: Weigh 40 g of fish maw glue and place it in a three-necked flask. Add 74 g of deionized water (the solid content of the liquefaction system is about 35%) and stir at 750 r / min to make it fully swell and disperse, thus obtaining mixture A. Adjust the pH of the system to 9.0 with 1 mol / L ammonia solution, heat to 50 ℃ and keep stirring for 60 min to fully liquefy the fish maw glue, thus obtaining liquefied fish maw glue solution B.

[0015] (2) 5-hydroxymethylfurfural grafting modification: 4 g of 5-hydroxymethylfurfural (10% of the mass of fish glue) was added to solution B and stirred at 60 °C for 2 h to obtain grafted modified fish glue solution C.

[0016] (3) Preparation and introduction of phytic acid-urea salt: Take another 13.2 g of 50% phytic acid aqueous solution (containing 0.01 mol of phytic acid) and 3.6 g of urea (0.06 mol, phytic acid:urea molar ratio 1:6) and mix them. Stir at 80 °C for 4 h to obtain a viscous, light yellow phytic acid-urea salt mother liquor D. Add the mother liquor D to solution C and stir evenly. Then, use 1 mol / L ammonia water to adjust the pH of the system back to 9.0 to obtain flame-retardant modified fish maw glue solution E.

[0017] (4) Epoxy crosslinking water-resistant modification: Add 4 g of trimethylolpropane triglycidyl ether (10% of the mass of fish maw glue) to solution E, stir and react at 70 °C for 2 h to obtain flame-retardant fish maw glue adhesive.

[0018] The obtained adhesive was applied to poplar veneer to prepare three-layer plywood, and then hot-pressed and cured at 120 ℃ for 6 min. Tests showed that the adhesive had a dry bond strength of 3.6 MPa, a wet bond strength of 1.5 MPa, and a wet strength retention rate of 42%. The limiting oxygen index of the cured film was 31%, the peak heat release rate in cone calorimetry was 165 kW / m², and the total heat release was 9.8 MJ / m², demonstrating significant flame retardant and water resistance effects.

Claims

1. A method for preparing a fish swim bladder adhesive that combines flame retardant and water-resistant properties, characterized in that, Includes the following steps: (1) Preparation of fish maw glue: Fish maw glue and deionized water are added to a three-necked flask. A reflux condenser, a magnetic stirrer and a thermometer are installed at the three necks of the three-necked flask respectively. The mixture is stirred thoroughly until the fish maw powder is evenly dispersed to obtain mixture A. The pH value of mixture A is adjusted with a weak acid and heated and stirred until the fish maw glue is liquefied at room temperature to obtain liquefied fish maw glue solution B. The solution is poured into a beaker and sealed for storage. (2) Preparation of flame-retardant fish maw glue: 5-hydroxymethylfurfural is added to the liquid fish maw glue solution B, and the mixture is heated and stirred under weakly alkaline conditions to allow the aldehyde group in 5-hydroxymethylfurfural to undergo a Schiff base condensation reaction with the amino group on the fish maw glue protein chain, thereby obtaining grafted modified fish maw glue solution C; phytic acid and urea are mixed and heated and stirred to obtain phytic acid-urea salt mother liquor D; the phytic acid-urea salt mother liquor D is added to the grafted modified fish maw glue solution C and stirred evenly to obtain flame-retardant modified fish maw glue solution E; (3) Epoxy crosslinking water-resistant modified fish maw glue: Triglycidyl ether epoxy compounds are added to the flame-retardant modified fish maw glue solution E, and the mixture is heated and stirred under weak alkaline conditions to allow the epoxy groups to undergo ring-opening crosslinking reactions with the amino, hydroxyl and carboxyl groups on the fish maw glue protein chain, thereby obtaining a fish maw glue adhesive that has both flame-retardant and water-resistant properties. Preferably, in step (1), the weight ratio of the fish maw glue to deionized water is 1:2 to 1:5, and the stirring speed is greater than 500 r / min; Preferably, in step (1), the weak acid is one or more of acetic acid, citric acid, and lactic acid; Preferably, in step (1), the adjusted pH value is 8 to 10, the heating temperature is 80°C to 100°C, and the liquefaction time is 60 min to 180 min; Preferably, in step (2), the amount of 5-hydroxymethylfurfural added is 5% to 15% of the mass of the fish maw glue; Preferably, in step (2), the temperature of the grafting modification reaction is 50 ℃ to 70 ℃, the reaction time is 1 h to 3 h, and the pH value of the reaction system is 8.5 to 9.5; Preferably, in step (3), the molar ratio of phytic acid to urea is 1:4 to 1:8; Preferably, in step (3), the reaction temperature for preparing phytic acid-urea salt mother liquor D is 60°C to 80°C, and the reaction time is 3 h to 4 h. Preferably, in step (3), the amount of phytic acid-urea salt mother liquor D added is 10% to 40% of the mass of fish glue, based on phytic acid-urea salt solids; Preferably, in step (3), after adding the phytic acid-urea salt mother liquor D to the grafted modified fish maw gel solution C, the pH value of the system is adjusted back to 8 to 9 using a weak acid or a weak base; Preferably, in step (4), the triglycidyl ether epoxy compound is one or two of trimethylolpropane triglycidyl ether and glycerol triglycidyl ether; Preferably, in step (4), the amount of the triglycidyl ether epoxy compound added is 5% to 20% of the mass of the fish maw glue; Preferably, in step (4), the pH value of the reaction system is 8 to 10, the reaction temperature is 60°C to 80°C, and the reaction time is 1 h to 6 h.